1. Field of the Invention
The present invention generally relates to a method of a silicide film in a semiconductor device, and more particularly to a method of a silicide film used in the manufacture of semiconductor integrated circuits such as schottky barriers, ohmic contacts and gate metallization.
2. Description of the Related Art
Generally, silicide films are compound of silicon and transition metal such as titanium(Ti), tantalium(Ta), tungsten(W), silver(Ag), and Gold(Ag), the films being used in the manufacture of semiconductor integrated circuits such as schottky barriers, ohmic contacts and gate metallization. These films are formed through a method of depositing one among the above mentioned transition metals on an objective layer of silicon or polysilicon layer, followed by thermal treatment at selected temeprature range and time range, or are formed through another method of forming silicide film directly on the objective layer.
Silicide film formed by any one of the above methods can be applied on top of a polysilicon layer used as bit lines or word lines, to form a layered structure called a "polycide" structure and it can also substitute polysilicon layer itself used as bit lines or word lines.
FIG. 1 is a partial sectional view of a semiconductor device in which tungsten silicide(WSi.sub.X) film is formed on a semiconductor substrate.
Referring to FIG. 1, in order to form WSi.sub.x film in accordance with a conventional technology using chemical vapor deposition method, a substrate 1 having an objective layer on which WSi.sub.x film is to be formed, is introduced into a reacting chamber and is set in the deposition zone of the reacting chamber. Afterwards, reactant gases including monosilane (SiH.sub.4) as source gas of silicon and tungsten hexa-fluoride (WF.sub.6) gas as source gas of tungsten are introduced into the reacting chamber, for the formation of WSi.sub.x film 2. At this time, the inside of the chamber is maintained at a specific temperature. The reactant gases is lastly supplied without the supply stop of the source gases until thickness of WSi.sub.x film approaches an objective value.
FIG. 2 shows AUGER analysis results of WSi.sub.x film deposited on polysilicon layer used as bit lines or word lines, horizontal axis being a sputter time taken in etching WSi.sub.x film from its surface to the bottom of the WSi.sub.x film and vertical axis being atomic concentration Si and W component in WSi.sub.x film formed.
Referring to FIG. 2, a mole ratio of tungsten to silicon(W:Si) in the WSi.sub.x film is not uniform through the thickness of the film. In further detail, in region II where the sputter time is about 6 seconds to 13 seconds, the ratio is 1:2.2-2.3 while in regions I and III, the ratio is 1:1.8-2.2, it being below the optimal range of 1:2.0-2.8. From the ratio obtained, the silicide films formed in regions I and III are assumed to be an unstable stoichiometry phase. On measuring the resistivity, the film does not have a desired value. Thus, the conventional method does not contribute to an enhancement in a characteristic of the semiconductor device.